KARAEV, M. T. On estimate for numerical radius of some contractions. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 58, n. 10, p. 1335–1339, 2006. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/3536. Acesso em: 6 dec. 2025.